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  • 1.
    Alexandersson, Martin
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department. Chalmers University of Technology, Sweden.
    Kjellberg, Martin
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Mao, W.
    Chalmers University of Technology, Sweden.
    Ringsberg, Jonas W
    Chalmers University of Technology, Sweden.
    Prediction of roll motion using fully nonlinear potential flow and ikeda’s method2021In: Proceedings of the International Offshore and Polar Engineering Conference, International Society of Offshore and Polar Engineers , 2021, p. 1670-1679Conference paper (Refereed)
    Abstract [en]

    Getting the best possible accuracy with the lowest possible computational cost is an important factor in the early design stage of ships. Potential flow-based analysis presents such a solution for seakeeping analyses. The accuracy of roll motion in potential flow is however not so good, due to the large influence from vicsous roll damping, which is missing in these calculations. This paper proposes a hybrid method, as a solution to this problem, where the viscous roll damping from Ikeda’s semi-empirical method is injected into an existing 3D unsteady fully nonlinear potential flow (FNPF) method. The hybrid method is investigated using roll decay tests with the KVLCC2 test case. This investigation shows that the accuracy of simulated roll motions is significantly improved and also shows good agreement with the corresponding roll decay model tests.

  • 2.
    Coslovich, Franciesco
    et al.
    Chalmers University of Technology, Sweden.
    Kjellberg, Martin
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Östberg, Magnus
    Flowtech International AB, Sweden.
    Janson, Carl-Erik
    Chalmers University of Technology, Sweden.
    Added resistance, heave and pitch for the KVLCC2 tanker using a fully nonlinear unsteady potential flow boundary element method2021In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 229, article id 108935Article in journal (Refereed)
    Abstract [en]

    In this paper, a fully nonlinear unsteady potential flow method is used to predict added resistance, heave and pitch for the KVLCC2 hull in regular head waves at design speed. The method presents a nonlinear decomposition of the velocity potential and the wave field and an adaptive grid refinement. A formulation for the acceleration potential is used to obtain the pressure. To improve computational efficiency, a Barnes-Hut algorithm is introduced. A grid dependency study and a study on the impact of different time steps on the solution are performed. Numerical results have been compared with experimental data for the design speed. A general good agreement is found for added resistance, especially for longer waves. Heave and pitch are properly computed for all wave lengths in the range λ/Lpp=0.4 to 1.4. © 2021 The Author(s)

  • 3.
    Gerhardt, Frederik
    et al.
    SSPA Sweden AB, Sweden.
    Kjellberg, Martin
    SSPA Sweden AB, Sweden.
    DETERMINING THE EEDI ‘WEATHER FACTOR’ fw2017Conference paper (Other academic)
    Abstract [en]

    The legislation on the Energy Efficiency Design Index (EEDI) requires determining a ‘weather factor’ fw that reflects how many percent of its calm water speed a ship can maintain in Beaufort 6 and corresponding waves. The higher the fw–value, the better the ship performs. In this paper we present and discuss a cost efficient way of experimentally finding the weather factor fw by means of wave tests in a seakeeping basin. To this end an evaluation software was developed to calculate fw from tests in both, regular and irregular waves in conjunction with calm water towing tank tests and wind tunnel experiments. Results show that the ‘fw standard curves’ from IMO Circular MEPC.1/Circ.796 are a useful tool to estimate an fw-value but are also very conservative i.e. the curves over-predict the speedloss in a seaway. Results from theoretical fw-calculations based on non-linear time domain seakeeping simulations are also presented and discussed

  • 4.
    Irannezhad, Mohsen
    et al.
    Chalmers University of Technology, Sweden.
    Bensow, Rickard E.
    Chalmers University of Technology, Sweden.
    Kjellberg, Martin
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Eslamdoost, Arash
    Chalmers University of Technology, Sweden.
    Comprehensive computational analysis of the impact of regular head waves on ship bare hull performance2023In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 288, article id 116049Article in journal (Refereed)
    Abstract [en]

    This paper focuses on investigating the impact of waves on ship hydrodynamic performance, enhancing our understanding of seakeeping characteristics and contributing to advanced ship and propeller design. It examines the resistance, motions, and nominal wake of the KVLCC2 bare hull, which is free to surge, heave, and pitch, in both calm water and regular head waves using a RANS approach. The research reveals a substantial dependency of the wake on grid resolution, particularly in calm water and shorter waves, while motions and resistance display a weaker dependency. The computed nominal wake is compared against towing tank SPIV measurements. Utilizing Fourier analyses and reconstructed time series, the study examines correlations among various factors influencing the bare hull’s performance in waves. The axial velocity component of the wake in waves demonstrates significant time variations, mainly driven by higher harmonic amplitudes. This dynamic wake is influenced by instantaneous propeller disk velocities due to hull motions, orbital wave velocities, boundary layer contraction/expansion, bilge vortex and shaft vortex dynamics. The wake distribution at the propeller plane not only differs significantly from the calm water wake in longer waves but also exhibits notably larger time-averaged values (up to 21%). 

  • 5.
    Irannezhad, Mohsen
    et al.
    Chalmers University of Technology, Sweden.
    Bensow, Rickard E
    Chalmers University of Technology, Sweden.
    Kjellberg, Martin
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Eslamdoost, Arash
    Chalmers University of Technology, Sweden.
    Towards Uncertainty Analysis of CFD Simulation of Ship Responses inRegular Head Waves2021In: Proceedings of the 23rd Numerical TowingTank Symposium, NuTTS 2021, 2021Conference paper (Refereed)
    Abstract [en]

    Ship hydrodynamic performance prediction in waves is a common practice in the early stages of the ship design process as the interaction between the ship and waves may adversely affect the hydrodynamic responses of the ship in comparison to calm water. Various well­established numerical and experimental methods are often utilized for prediction of ship performance in waves. Although the model tests are expensive and time­consuming, a high level of accuracy is often achieved in such experiments. On the other hand, with respect to the increased computational power, prediction of ship performance in waves by the numerical methods based on Computational Fluid Dynamics (CFD) techniques are gradually acquiring more popularity. However, the validity of the incorporated discretization schemes and modelling assumptions in these state­of­the­art CFD methods are often overlooked and the method accuracy is mainly assessed through the validation of the results based on the respective model test data. Validation as an engineering exercise aims to show that the right equations are solved, while verification (mathematical exercise) is required to demonstrate that equations are solved right [1]. The eventual objective of this research is to perform verification and validation exercises of a ship performance prediction in regular head waves using CFD, whereas in this paper, the working progress is presented which may be subjected to significant revisions. To this end, extensive attempts have been made to investigate numerical wave propagation without the presence of the hull. Ship responses in waves are significantly influenced by the wave excitation forces. Therefore, not only high level of accuracy is required for the simulation of the numerical waves, but also quantification of the numerical uncertainties are of a great importance. This becomes even more challenging when the ship hydrodynamic responses, such as motions and added resistance in waves, exhibit dependencies on wave steepness. In this paper, the main focus of such uncertainty analyses is on the systematic grid convergence study.

  • 6.
    Irannezhad, Mohsen
    et al.
    Chalmers University of Technology, Sweden.
    Eslamdoost, Arash
    Chalmers University of Technology, Sweden.
    Kjellberg, Martin
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Bensow, Rickard
    Chalmers University of Technology, Sweden.
    Investigation of ship responses in regular head waves through a Fully Nonlinear Potential Flow approach2022In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 246, article id 110410Article in journal (Refereed)
    Abstract [en]

    In this study, the hydrodynamic performance of a ship in terms of motions and resistance responses in calm water and in regular head waves is investigated for two loading conditions using a Fully Nonlinear Potential Flow (FNPF) panel method. The main focus is understanding the ship responses in a broad range of operational conditions. Comprehensive analyses of the motions and their correlation with the wave making resistance including their harmonics in waves are presented and compared against experimental data. The predicted motions compare well with experimental data but the resistance prediction is not quite as good. The natural frequencies for heave and pitch are estimated from a set of free decay motion simulations in calm water to provide a better insight into the ship behavior near resonance conditions in waves. Interestingly, in addition to the well known peak in the added wave resistance coefficient around wave lengths close to one ship length, a secondary peak is detected in the vicinity of wave lengths with half the ship length. © 2022 The Authors

  • 7.
    Kjellberg, Martin
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Gerhardt, Frederik
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Werner, Sofia
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Sailing in waves: A numerical method for analysis of seakeeping performance and dynamic behavior of a wind powered ship2022In: SNAME 24th Chesapeake Sailing Yacht Symposium, CSYS 2022, Society of Naval Architects and Marine Engineers , 2022Conference paper (Refereed)
    Abstract [en]

    Before the background of the internationl Maritime Organization's 2050 emission reducation targets, the largest sailing ship in the world is currently being developed in Sweden. This wind powered car carrier, called Oceanbird, will have four 80-metre-high wing sails targeting CO2savings in the order of 90%. The prediction and analysis of the seakeeping performance of such a ship is of importance, not only in terms of sailing dynamics, but also when it comes to the structural design of the rig. To this end, a numerical method for predicting a ship's motions and loads on its rigid wing sails is described in this paper and a demonstration of how the method can be used to obtain such loads is presented. The numerical method is based on an unsteady 3D fully nonlinear potential flow hydrodynamic model coupled with a hybrid 2D RANS/3D lifting-line aerodynamic model. Simulations in a seaway with short-crested irregular waves and corresponding wind conditions are conducted, resulting in time histories of the aerodynamic and inertial forces acting on the rig. Possible applications of the method include fatigue analysis of the wing sails, where the accumulated fatigue damage over the lifespan of the rig structure depends on the sum of aerodynamic forces and motion induced inertial forces. Other potential applications include sail dynamics, parametric roll, sheeting strategies and appendage configuration studies. 

  • 8.
    Kontos, S
    et al.
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Lundbäck, Olov
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Kjellberg, Martin
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Wilske, E
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Werner, Sofia
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Manoeuvre simulations in design process of wind powered vesselConference paper (Other academic)
    Abstract [en]

    Wind propulsion systems (WPS) are one of the most promising technologies for ship propulsion that can radically reduce greenhouse gas emissions. However, attention must be paid to the additional transversal forces and yaw moments connected to a wind propulsion system, as it can affect the manoeuvring and seakeeping performance of a ship. This paper demonstrates how time-domain simulations can be utilised to assess the manoeuvrability of a wind powered vessel to support the decision making, from the early design stage, all the way to testing the control systems, design of Human Machine Interface (HMI) and developing crew guidelines and training. The manoeuvre simulations are carried out with SSPA’s six degree of freedom inhouse code, SEAMAN-Winds. We present firstly a validation against manoeuvring model tests of a wind powered ship, where the wind propulsion units are represented by pulling fans. VPP calculations, which are commonly used in the early design phase, can predict the rudder angle required to balance the side force and yaw moment from the wind propulsion system. However, such steady-state computations provide no information on how robust this balance is when dynamic effects are present (e.g., wind gusts) and whether the balance can be regained if it has been momentarily lost. Therefore, time-domain simulations are shown to be useful to assess whether a ship can sail safely close to the limits of its VPP polars. Furthermore, it is demonstrated how mariners operating a real-time manoeuvre simulation tool can be utilised to increase the proof-of-concept, assess the HMI design, and for crew training.

  • 9.
    Orych, Michal
    et al.
    Chalmers University of Technology, Sweden; FLOWTECH International AB, Sweden.
    Östberg, Magnus
    FLOWTECH International AB, Sweden.
    Kjellberg, Martin
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Werner, Sofia
    RISE Research Institutes of Sweden, Safety and Transport, Maritime department.
    Larsson, Lars
    Chalmers University of Technology, Sweden; ISYD AB International School of Yacht Design, Sweden.
    Speed and delivered power in waves — Predictions with CFD simulations at full scale2023In: Ocean Engineering, ISSN 0029-8018, E-ISSN 1873-5258, Vol. 285, article id 115289Article in journal (Refereed)
    Abstract [en]

    An efficient numerical method is proposed to estimate delivered power and speed loss for a ship in wind and waves. The added resistance in waves, obtained with an unsteady potential flow panel method, is added to the calm water resistance from a steady-state potential flow/RANS method coupled with a body force propeller model for self-propulsion. A comparison of numerical and experimental results is made for added resistance, calm water resistance and delivered power. A good agreement is obtained. As a practical application, the approach is used to calculate the weather factor, fw, of the Energy Efficiency Design Index (EEDI). The calculated weather factor is consistent with the values derived from full-scale measurements included in a database of similar ships. © 2023 The Author(s)

  • 10. Wigren, I.
    et al.
    Kjellberg, Martin
    SSPA Sweden AB, Sweden.
    Gerhardt, Frederik
    SSPA Sweden AB, Sweden.
    How much is enough?: EEDI rules and 'minimum propulsion power'2020In: Naval architect, ISSN 0306-0209, no August, p. 22-25Article in journal (Refereed)
    Abstract [en]

    Since the introduction of the EEDI almost a decade ago, slow steaming and the wish to reduce bunkering costs have resulted in a trend towards less powerful engines. To avoid vessels becoming underpowered and unsafe, IMO has published guidance on the 'Minimum Propulsion Power to Maintain the Manoeuvrability of Ships in Adverse Conditions'. A group of seakeeping experts from SSPA Sweden AB explains the rules.

1 - 10 of 10
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